Recent advances in microelectronics have included the use of high-k films in gate dielectric stacks for logic applications. To increase device reliability and reduce electron leakage from the gate electrode to the transistor channel, semiconductor transistor technology is introducing high dielectric constant (high-k) materials that allow increased physical thickness of the gate dielectric layer. Dielectric materials featuring a dielectric constant greater than that of SiO2 (k˜3.9) are commonly referred to as high-k materials. An early motivation for seeking high-k films for use in metal-oxide field effect transistors (MOSFETs) was one of simply reducing the leakage current without reducing the film capacitance. Furthermore, for many applications, the high-k films need to have the electrical equivalent of a SiO2 layer having a physical thickness, Tox, of about 1 nm.
The presence of a thin dielectric interface layer between a high-k film and an underlying substrate may be highly beneficial to preserve interface state characteristics and form an interface with good electrical properties. The quality of the interface layer can affect device performance, as the interface layer is intimately connected to the channel of the transistor. However, the presence of an interface layer lowers the overall dielectric constant of the gate stack and, therefore, the interface layer may need to be thin.
Many high-k films can catalytically promote growth of a thick interfacial SiO2 layer between the high-k film and a Si substrate during deposition of the high-k film and/or during post-deposition annealing, thereby increasing Tox to unacceptable levels. When a capacitance corresponding to a total SiO2 thickness of about one nm is needed for the replacement of SiO2 gate dielectric in MOSFETs with a high-k film, such low-k reaction layers in series with the desired high-k film, can rapidly nullify the benefits of the high-k film.
Accordingly, further developments are required to solve these and other problems associated with integration of high-k films into semiconductor devices.